Pressure sensor plate having a plurality of measuring diaphragms distributed in a matrix

ABSTRACT

A device for measuring various fluid pressures, the device includes a sensor plate which has fastening holes, which are distributed in matrixlike fashion over the sensor plate. Measuring diaphragms, which form end walls of blind bores in the sensor plate, are located between the fastening holes. Through fluid conduits of a hydraulic block to which the sensor plate can be secured, the measuring diaphragms can be acted upon by pressure. The evaluation is done with four strain gauges applied to each measuring diaphragm, the strain gauges being interconnected to form a Wheatstone bridge. Because it is possible to mount the sensor plate in a way that optimizes strain, it is possible to measure various pressures with minimal measurement error using one sensor plate.

This application is a 371 of PCT/EP96/01807 filed Apr. 30, 1996.

PRIOR ART

The invention relates to a device for measuring a plurality of fluidpressures. It is intended in particular for mounting on a hydraulicblock that is used for hydraulic control of a vehicle brake system.

In hydraulic external-force brake systems, which are equipped with anelectrically driven hydraulic pump for generating fuel pressure, it isnecessary to measure the brake fluid pressure in wheel brake cylindersand at other points in the brake system such as in a master cylinder ora hydraulic reservoir.

It is known to measure the brake fluid pressure at the various points ofthe brake system using one pressure sensor each, which is mounted at therespective point or centrally on the hydraulic block and communicateswith the various points of the brake system over hydraulic lines. Thishas the disadvantage of major construction effort and expense.

ADVANTAGES OF THE INVENTION

The pressure measuring device of the invention has a sensor plate with aplurality of measuring diaphragms for measuring various pressures. It isintended especially for hydraulic vehicle brake systems, but can be usedequally well for measuring the pressures of any arbitrary fluids. Themeasuring diaphragms are distributed uniformly in matrixlike fashion onthe sensor plate. They can be located for instance at the corners ofimaginary equilateral triangles (triangular matrix) or squares (squarematrix), or may for instance be distributed equidistantly on one or moreimaginary concentric circles.

Fastening devices of the sensor plate, such as screw holes, are arrangeduniformly around each measuring diaphragm, and as a result individualfastening devices are simultaneously surrounded by a plurality ofmeasuring diaphragms. Each measuring diaphragm is surrounded by an equalnumber of fastening devices, which are preferably all spaced equallyapart from the respective measuring diaphragm. For instance, if themeasuring diaphragms and fastening devices are disposed on triangularmatrixes or square matrixes, each measuring diaphragm is located in themiddle of an imaginary equilateral triangle or square, whose corners areformed by the fastening devices that surround the measuring diaphragm.In an equidistant arrangement of the measuring diaphragms on a circle,one fastening device is for instance located in the middle of thecircle, and a number of fastening devices that equals the number ofmeasuring diaphragms is disposed on a center bisector between each twomeasuring diaphragms, on a concentric circle surrounding the measuringdiaphragms, so that each measuring diaphragm is located between eachgroup of three fastening devices.

The invention has the advantage that a requisite number of measuringdiaphragms can be accommodated in a simple way all on the same sensorplate. The mounting and sealing of the sensor plate, for instance on ahydraulic block, are simple and can be accomplished quickly; thepressure sensors required can be manufactured economically. Themeasuring diaphragms are nearly strain-free, which is a prerequisite foraccurate measurements with minimal error over a long period of use. Bymeans of the matching disposition of each measuring diaphragm betweenthe same number of fastening devices, the measuring diaphragms aredeformed identically when pressure is imposed, so that for the samepressure, each measuring diaphragm furnishes an identical measurementsignal.

Another advantage of the invention is that the measuring diaphragms ofthe sensor plate, which are disposed close together, and the selecteddisposition of the measuring diaphragms relative to one another makerapid electrical contacting with a central evaluation circuit possible,which again increases the precision of measurement. In particular, plugconnections and long cables between the measuring diaphragms and theevaluation circuit, which from corrosion and aging can lead to elevatedtransition resistances and can make the outcome of measurement wrong,are unnecessary.

To measure the fluid pressures, preferably elongatable electricalresistors are mounted on the outside or inside of each measuringdiaphragm. These resistors deform elastically along with the measuringdiaphragm from being acted upon by the fluid whose pressure is to bemeasured, and this causes them to change their electrical resistance.This change in resistance is utilized for ascertaining the fluidpressure. Strain gauges, for instance, may be applied as elongatableelectrical resistors to the measuring diaphragms using thin-film,thick-film or foil technology.

To reduce the measurement error, four elongatable electrical resistorsare mounted on each measuring diaphragm, and are interconnected as aso-called full bridge (Wheatstone bridge); as a result, changes inresistance caused by temperature changes, for instance, can becompensated for.

The disposition of the four full bridge resistors can also be used toimprove the outcome of measurement. Two resistors are disposed in themiddle of each measuring diaphragm, and the two other resistors aredisposed diametrically opposite, on the circumference of the measuringdiaphragm. These are the zones of greatest oppositely orientedmechanical strains. The elongation directions of the four resistors areparallel to one another and to an imaginary diameter line through thetwo resistors disposed on the circumference of the measuring diaphragm.One outer resistor each is connected in series with one middle resistor.By this arrangement of the four bridge resistors, maximum pressuresensitivity of the bridge circuit is achieved.

With a generally flat sealing element with one-piece O-rings, blindbores that contain the measuring diaphragms in the sensor plate can besealed off, from the hydraulic block, for example, with minimal effortand expense. Surfaces of the sensor plate and of the hydraulic blockthat face one another need not be provided with recesses into whichsealing rings can be placed. The generally flat sealing element is usedto position the O-rings during assembly. It does not have to be presentover the entire surface of the sensor plate; webs that connect theO-rings to one another are sufficient.

BRIEF DESCRIPTION OF THE DRAWING

The pressure measuring device of the invention will be described belowin terms of two exemplary embodiments shown in the drawing. Shown are:

FIG. 1, a round sensor plate according to the invention, shown insection and in perspective;

FIG. 2, an enlarged detail of FIG. 1;

FIG. 3, a rectangular sensor plate, shown in section, in a secondembodiment of the invention;

FIG. 4, a sectional view of a pressure measuring device of theinvention;

FIG. 5, a perspective view of the pressure measuring device of FIG. 4;

FIG. 6, an exploded view of the pressure measuring device of FIG. 4; and

FIG. 7, an electrohydraulic vehicle brake system of the invention.

The drawings are to various different scales.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The pressure measuring device 10 according to the invention, shown inFIG. 1, has a circular sensor plate 12 made of metal. It may alsocomprise ceramic, for example. It has a total of seven screw holes 14,16 as fastening devices for mounting the sensor plate 12 to some othercomponent. One of the screw holes 16 is located in the middle of thesensor plate 12, while the other six screw holes 14 are locatedequidistant from one another, near the edge, at the circumference of thesensor plate 12. The screw holes 14 near the edge have the same spacingfrom the middle screw hole 16 as from each of the adjacent screw holes14 near the edge. At the center point of an imaginary triangle, whosecornersare formed by two adjacent screw holes 14 near the edge and bythe middle screw hole 16, there is a single measuring diaphragm 18.Because of this distribution of the screw holes 14, 16 and measuringdiaphragms 18 on the sensor plate 12, the measuring diaphragms 18 remainvirtually strain-free when the sensor plate 12 is mounted on acomponent. Any residual strain that may be present despite thisstrain-optimizing placement has the same effect in each measuringdiaphragm 18, because of the matching arrangementof each measuringdiaphragm 18 in the middle between three screw holes 14, 16. Slighterrors in measurement from such residual strains are thus the same forall six measuring diaphragms 18, and thus for the same measured values,the same pressure prevails at the measuring diaphragms 18.

The measuring diaphragms 18 are integral with the sensor plate 12 (FIG.2);they are formed by a blind bore 20 from a fastening side 22 of thesensor plate 12, which side comes to rest on a component to which thesensor plate 12 is fastened. The blind bores 20 may for example bedrilled, or ifthe sensor plate 12 is a sintered part they may be made inthe course of the sintering process. An end wall of the blind bores 20forms the measuring diaphragms 18. The diaphragm diameter is 10 mm. Thediaphragm thickness, in the exemplary embodiment, is between 0.5 and 1mm, dependingon the pressure the pressure measuring device of theinvention is intended to measure and on the bursting pressure that themeasuring diaphragms 18 must withstand. In the exemplary embodiment, themeasurement pressure is up to 250 bar, and the rated bursting pressureis 1200 bar.

Four strain gauges 24, 25 are applied to each measuring diaphragm 18 bythin-film, thick-film or foil technology; of them, two strain gauges 24are located diametrically opposite one another in the peripheral regionofthe measuring diaphragms 18, and the other two strain gauges 25 aredisposed next to one another in the center of the measuring diaphragms.All four strain gauges 24, 25 are parallel to one another and aredisposedwith their longitudinal and elongation direction parallel to animaginary diameter line through the two peripherally located straingauges 24. If the measuring diaphragm 18 is deformed upon the impositionof pressure, the strain gauges 24, 25 elongate or are upset, and theychange their electrical resistance, and this is utilized to ascertainthe pressure. By means of conductor tracks, the resistors 24, 25 areinterconnected to forma full bridge (Wheatstone bridge) and areelectrically conductively connected to four terminal contacts 28.

FIG. 3 shows a second embodiment of a sensor plate 30 of a pressuremeasuring device according to the invention. The sensor plate 30 isrectangular; a total of six measuring diaphragms 18 with resistorbridges 24, 25 mounted on them are disposed in two rows side by side,the rows being offset by half the spacing between two measuringdiaphragms 18; thatis, the measuring diaphragms 18 of one row face thegaps between measuring diaphragms 18 in the other row. In this way, eachmeasuring diaphragm is spaced apart by the same distance from theadjacent measuring diaphragms 18 and are located at the corners ofimaginary equilateral triangles.

Between and around the six measuring diaphragms 18, screw holes 32 arearranged in the manner of a triangular matrix of equilateral triangles.The measuring diaphragms 18 are accordingly, as in the round sensorplate 12, located in the middle of an imaginary equilateral triangle,whose corners are formed by three screw holes 32.

With the exception of the shape of the sensor plate 30 and thedisposition of the measuring diaphragms 18 and screw holes 32, thissensor plate matches the sensor plate 12 shown in FIG. 1 and functionsin the same way.To avoid repetition, the descriptions of FIGS. 1 and 2therefore apply to this extent. Below, the pressure measuring device ofthe invention will bedescribed in terms of the rectangular sensor plate30, but the description applies correspondingly to the round sensorplate 12 as well.

FIGS. 4 and 5 show a pressure measuring device of the invention, inwhich the rectangular sensor plate 30 is screwed to a hydraulic block 34by means of screws 36 passed through the screw holes 32 of the sensorplate 30. The section shown in FIG. 4 through the pressure measuringdevice of the invention extends in alternation through a screw hole 32and through ablind bore 20 of a measuring diaphragm 18, although in factthese are in two different planes. One fluid conduit 38, through which ameasuring diaphragm 18 can be acted upon by fluid, discharges into eachof the blindbores 20. For sealing purposes, a sealing plate 40 isinserted between the sensor plate 30 and the hydraulic block 34 (seeFIG. 6) and has O-rings 42, integral with it, that it positions at theblind bores 20 of the measuring diaphragms 18. When the sealing plate 40is not yet installed, acord diameter of the O-rings 42 is greater thanthe thickness of the sealing plate 41.

To measure the electrical resistances of the strain gauges 24, 25 and toascertain the pressure prevailing in the blind bores 20 on the bases ofthe resistances, the terminal contacts 28 of the strain gaugemeasurement bridges 24, 25 are connected to an evaluation circuit 46 bythick-wire bonds 44, or in other words aluminum wires that are connectedto the terminal contacts 28 by friction welding. The evaluation circuit46 is mounted on a flat substrate 48, which in plane view has the shapeof a double T and is screwed by its stem, extending with slight spacingabove the sensor plate 30, to the hydraulic block 34. The terminalcontacts 28 are located, freely accessible, close to one edge of thesubstrate 48 on the sensor plate 30. This is also applicable if theround sensor plate 12,shown in FIG. 1, is used, in which the terminalcontacts of three measuringdiaphragms 18 are each located on a straightline. The evaluation circuit 46 is located in the center of the sixmeasuring diaphragms 18, resulting in short electrical connection paths,preferably of equal length, from thestrain gauges 24, 25 to theevaluation circuit 46. This makes accurate pressure measurements withminimal errors possible.

The evaluation circuit 46 can evaluate the resistances of the straingauges24, 25 of all six measuring diaphragms 18. In one embodiment ofthe invention, the resistances of the strain gauges 24, 25 of themeasuring diaphragms are measured and evaluated in succession in amultiplexing mode, so that the resistances of all six measuringdiaphragms 18 are thus evaluated by the same electronic components. As aresult, different outcomes of measurement when the pressure conditionsat different measuring diaphragms 18 are the same are averted.

In FIG. 7, a hydraulic vehicle brake system of the invention using thepressure measuring device described is shown. The vehicle brake systemhastwo brake systems, supplementing one another, namely one servicebrake system, which generates brake fluid pressure by means of ahydraulic pump 50 and acts on wheel brake cylinders 52, 54 of all thevehicle wheels, andan auxiliary brake system, which draws its brakefluid pressure from a pedal-actuated master cylinder 55, and which actson the wheel brake cylinders 52 of only two vehicle wheels.

Each wheel brake cylinder 52, 54 has one first shutoff valve 56, whichis open in its basic position, and one second shutoff valve 58, which isclosed in its basic position.

When a brake pedal 62 of the master cylinder 55 is actuated, a pedalposition sensor 64 and a pressure sensor 74 output an electrical signaltoa control circuit, not shown, for the brake system that controls bothall the valves and an electric pump motor 66 of the vehicle brake systemof the invention. The second shutoff valves 58 are opened, and in thisway the wheel brake cylinders 52, 54 are acted upon by pressure from ahydraulic reservoir 68, which in turn is put under pressure by thehydraulic pump 50, so that brake fluid under pressure is available evenifthe hydraulic pump 50 is not in operation. The pressure in thehydraulic reservoir 68 is monitored by a pressure sensor 72. A pressurelimiting valve 60 guards the hydraulic reservoir 68 against overloading.Once a brake fluid pressure in the wheel brake cylinders 52, 54 isreached, whichis dependent on the pressure generated with the mastercylinder 55, the second shutoff valves 58 are closed. The first shutoffvalves 56 are closed in this case, so that no brake fluid can escapethrough them from the wheel brake cylinders 52, 54 during braking withthe service brake system.

The brake fluid pressure in the wheel brake cylinders 52, 54, the mastercylinder 55, and the hydraulic reservoir 68 is delivered to themeasuring diaphragms 18 through lines and through the fluid conduits 38in the hydraulic block 34. The measuring diaphragms 18, with the straingauges 24, 25 applied to them and with the evaluation circuit 46, formpressure sensors 70. 72, 74. Their signal is delivered to the controlcircuit of the vehicle brake system of the invention.

If the brake fluid pressure in the wheel brake cylinders 52, 54 ishigher than what corresponds to the pressure generated by the mastercylinder 55 and measured with the pressure sensor 74, then brake fluidpressure is reduced by opening the first shutoff valves 56 in the wheelbrake cylinders 52, 54, and brake fluid flows into a tank 76 of themaster cylinder 55.

If there is a problem in the service brake system and an inadequatebrake pressure prevails in the hydraulic reservoir 58, then uponactuation of the brake pedal 62 the first shutoff valves 56 of all fourwheel brake cylinders 52, 54 remain open, and the second shutoff valves58 remain closed. The two wheel brake cylinders 52 that are connected tothe auxiliary brake system are acted upon with pressure by the mastercylinder55, through a master cylinder shutoff valve 78 which is open inits basic position and is closed when the service brake system is inuse, and which then disconnects the master cylinder 55 from the wheelbrake cylinders 52,54 and from the brake system.

When the service brake system is in use, a return valve 80, which isclosedin its basic position, is opened. Through the opened return valve80, brakefluid can flow out of the two wheel brake cylinders 52connected to the auxiliary brake system and back into the tank 76 of themaster cylinder 55when the first shutoff valves 56 are opened. When theauxiliary brake system is in use, the closed return valve prevents areturn flow of brake fluid from the master cylinder 55 into the tank 76.

Via a shutoff valve 82, which is closed in its basic position, a travelsimulator 84, known per se, is connected to the master cylinder 55; in amanner known per se, this travel simulator can hold brake fluid as afunction of the pressure, so that when the service brake system is beingused and the auxiliary brake system, actuated by the master cylinder 55,the driver will have the familiar feel of the brake pedal, in which thebrake pedal 62 yields as a function of the foot power exerted.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

I claim:
 1. A device for measuring a plurality of fluid pressures, whichcomprises a sensor plate (12, 30) with a plurality of measuringdiaphragms (18), which can be acted upon from one side by the fluid tobe measured, through fluid conduits (38) of a component (34) on whichthe sensor plate (12, 30) can be mounted, the measuring diaphragms (18)are distributed in matrixlike fashion on the sensor plate (12, 30); thesensor plate (12, 30) has fastening devices (14, 16, 32) for mountingsaid sensor plate on the component (34), said measuring diaphragms aredistributed in matrixlike fashion on the sensor plate (12, 30) in such away that in each case there is one measuring diaphragm (18) locatedapproximately in a middle between an equal number of fastening devices(14, 16, 32).
 2. A device in accordance with claim 1, in which themeasuring diaphragms (18) are embodied as end walls of blind bores (20)in the sensor plate (12, 30).
 3. A device in accordance with claim 1, inwhich the measuring diaphragms (18) are integral with the sensor plate(12, 30).
 4. A device in accordance with claim 2, in which the measuringdiaphragms (18) are integral with the sensor plate (12, 30).
 5. A devicein accordance with claim 1, in which at least one elongatable electricalresistor (24, 25) is applied to each measuring diaphragm (18), and alength of said resistor and at the same time its electrical resistancechanges upon deformation of the measuring diaphragm (18).
 6. A device inaccordance with claim 2, in which at least one elongatable electricalresistor (24, 25) is applied to each measuring diaphragm (18), and alength of said resistor and at the same time its electrical resistancechanges upon deformation of the measuring diaphragm (18).
 7. A device inaccordance with claim 3, in which at least one elongatable electricalresistor (24, 25) is applied to each measuring diaphragm (18), and alength of said resistor and at the same time its electrical resistancechanges upon deformation of the measuring diaphragm (18).
 8. A device inaccordance with claim 5, in which four elongatable electrical resistors(24, 25) are applied to each measuring diaphragm (18) and areinterconnected to form a full bridge circuit.
 9. A device in accordancewith claim 8, in which two resistors (24) are disposed in a middle ofone measuring diaphragm (18), and two other resistors (24) are disposeddiametrically opposite one another on a circumference of the measuringdiaphragm (18), wherein the elongation directions of the four resistors(24, 25) extend parallel to a diameter line through the two outerresistors (24), and wherein one outer resistor (24) each is connected inseries with one middle resistor (25).
 10. A device in accordance withclaim 5, in which said device has one common electronic evaluationcircuit (46) for the resistors (24, 25) of all the measuring diaphragms(18) of the sensor plate (12, 30).
 11. A device in accordance with claim8, in which said device has one common electronic evaluation circuit(46) for the resistors (24, 25) of all the measuring diaphragms (18) ofthe sensor plate (12, 30).
 12. A device in accordance with claim 9, inwhich said device has one common electronic evaluation circuit (46) forthe resistors (24, 25) of all the measuring diaphragms (18) of thesensor plate (12, 30).
 13. A device in accordance with claim 10, inwhich the measuring diaphragms (18) in the sensor plate (12, 30) arecovered by a flat substrate (48) for the electronic evaluation circuit(46); that terminal contacts (28) of the electrical resistors (24, 25)applied to the measuring diaphragms (18) are located on the sensor plate(12, 30) freely next to an edge of the substrate (48) and communicatewith the electronic evaluation circuit (46) via electrical connectionmeans (44).
 14. A device in accordance with claim 10, in which theevaluation circuit (46) operates in a multiplexing mode.
 15. A device inaccordance with claim 13, in which the evaluation circuit (46) operatesin a multiplexing mode.
 16. A device in accordance with claim 2, inwhich between the sensor plate (12, 30) and the component (34) that hasthe fluid conduits (38), a generally flat sealing element (40) isinserted, said sealing elements includes O-rings (42), integral with it,that encompass orifices of the blind bores (20) in the sensor plate (12,30), and which has fluid passage openings inside the O-rings (42).
 17. Adevice in accordance with claim 3, in which between the sensor plate(12, 30) and the component (34) that has the fluid conduits (38), agenerally flat sealing element (40) is inserted, said sealing elementsincludes O-rings (42), integral with it, that encompass orifices of theblind bores (20) in the sensor plate (12, 30), and which has fluidpassage openings inside the O-rings (42).
 18. A device in accordancewith claim 5, in which between the sensor plate (12, 30) and thecomponent (34) that has the fluid conduits (38), a generally flatsealing element (40) is inserted, said sealing elements includes O-rings(42), integral with it, that encompass orifices of the blind bores (20)in the sensor plate (12, 30), and which has fluid passage openingsinside the O-rings (42).
 19. A device in accordance with claim 8, inwhich between the sensor plate (12, 30) and the component (34) that hasthe fluid conduits (38), a generally flat sealing element (40) isinserted, said sealing elements includes O-rings (42), integral with it,that encompass orifices of the blind bores (20) in the sensor plate (12,30), and which has fluid passage openings inside the O-rings (42).